Macro study of the skeletal material, ongoing. Tabulae.

Other closeups of Skeletal Material

Images of ampullae are found in a previous post.

Earlier images of tabulae and coenosteum are found in a previous post, here.

Tubes: fossil houses of polyps, with tabulae:

Fragment of Millepora platyphylla, with fracture exposed.

A compelling  description of formation of tabulae in Millepora is found in Kaestner's  Invertebrate Zoology:

The polyps stand in little pits into which they can contract. In many species, five to eight defensive zooids form a circle, 0.25 mm in diameter, around a feeding zooid. New growth slowly thickens the crust while the lower layers die. As the polyps grow outward within their tubes, their aboral surfaces produce a new calcareous layer.

Focus stack of fracture, showing tabulae.

General appearance of surface, with irregular cyclosystems:

Kaestner again:

The polyps stand in little pits into which they can contract. In many species, five to eight defensive zooids form a circle, 0.25 mm in diameter, around a feeding zooid.